1. Field of the Invention
The present invention relates to an enzyme electrode to electrically measure through an enzyme reaction a concentration of a specified chemical material contained in a liquid to be examined and serving as a substrate of the enzyme. The invention also relates to a method of manufacturing such an enzyme electrode.
2. Prior Art Statement
As a conventional enzyme electrode, such an enzyme electrode as shown in FIG. 1e has been known. A structure of this conventional enzyme electrode will be described together with its manufacturing method with reference to FIGS. 1a to 1e.
FIG. 1a shows a state in which lead wires 110 are connected to a working electrode 105 and a reference electrode 106 by soldering, respectively. The working electrode 105 is made of platinum and is formed like a pin having a circular cross section. The reference electrode 106 is made of silver and is formed like a cylinder having a hollow portion 106b.
FIG. 1b shows a state in which the working electrode 105 and reference electrode 106 are enclosed in a cup-shaped casing 109. The reference electrode 106 is inserted into the casing 109 from an opening 109a of the casing 109. The working electrode 105 is supported by a supporting member 107 in the hollow 106b of the reference electrode 106 so as to be insulated from the reference electrode 106. The reference electrode 106 and working electrode 105 are coaxially arranged. Lead wires 110 are pulled out to the outside from a hole 109b formed on the bottom portion of the casing 109.
FIG. 1c shows a state in which an epoxy resin 108 is filled in the casing 109. The epoxy resin 108 overflows on the opening portion 109a of the casing 109, thereby completely covering the working electrode 105 and reference electrode 106. It takes about six days at room temperature until the epoxy resin is hard.
FIG. 1d shows a state in which the upper surface of the assembly shown in FIG. 1c is ground and polished together with the casing 109 and worked so as to form a spherical surface, the edge surfaces of the working electrode 105 and reference electrode 106 are exposed, and these edge surfaces are used as exposed portions 105a and 106a, respectively. A diameter of working electrode 105 and inner and outer diameters of reference electrode 106 are determined such that the ratio of the areas of the exposed portions 105a and 106a become a predetermined value.
FIG. 1e shows an enzyme electrode which is completed by attaching an immobilized enzyme film 111 to the assembly shown in FIG. 1d. The film 111 is made by immobilizing an enzyme (e.g., glucose oxidase or the like) to detect a specified chemical material serving as a substrate to a high molecular film. The film 111 is coated onto the polished surface so as to be closely adhered to the exposed portions 105a and 106a. The peripheral edge portion of the film 111 is fixed to the outer surface of the casing 109 by an O ring 112. A groove 109c to fix the O ring 112 is formed in the outer peripheral surface of the casing 109.
The foregoing conventional enzyme electrode is produced one by one by the hand work and its mass production is difficult. In addition, this hand work consists of continuous fine works and has drawbacks such that the material is damaged or left in vain, in particular, the electrode material is frequently damaged and a large amount of electrode material is left in vain and the yield is low. Further, there are inconveniences such that the working cost and manufacturing costs are high. The working cost occupies 60 to 80% of the manufacturing cost.
In addition, since the immobilized enzyme film 111 used is provided to integrally cover the exposed portions 105a and 106a of both electrodes, the film 111 having a large area is necessary. There is an inconvenience such that the final cost of the enzyme electrode rises because the immobilized enzyme film itself is expensive.
On the other hand, the foregoing conventional enzyme electrode has the following problems when it is used.
When the exposed portions 105a and 106a are formed by grinding and polishing, cracks and gaps are formed in the epoxy resin 108 around the working electrode 105. This is because of the differences of hardness among the epoxy resin 108, working electrode 105, and reference electrode 106. If the water or other liquid enters the cracks or graps when the enzyme electrode is used, the noise is generated and the measuring accuracy deteriorates.
An output of the enzyme electrode is determined by the areas of the exposed portions 105a and 106a (especially, the area of the exposed portion 105a of the working electrode 105). The exposed portions 105a and 106a are made by the hand work, so that a variation of areas of the exposed portions 105a and 106a occurs and the outputs also vary.
Further, an output variation is caused due to the defective attachment of the immobilized enzyme film 111.
Since one kind of immobilized enzyme film 111 is attached, the foregoing conventional enzyme electrode has an inconvenience such that it cannot be used to measure many items.
There are also inconveniences such that the foregoing conventional enzyme electrode is cylindrical and a degree of freedom of the shape is small, there is a limitation when designing an apparatus for clinical examinations or the like using this enzyme electrode, namely, the easiness of use of such an enzyme electrode is poor, and the like.